Purpose
The ability to measure different diffusion rates along different spatial directions is a unique feature that distinguishes diffusion tensor imaging (DTI) from other MRI techniques. To improve this method it is necessary to identify potential error sources and to minimize their influences. In this study the influence of the imaging gradients on the b-values as well as an optimal application scheme for the necessary six different diffusion gradient directions were experimentally and analytically investigated.
Methods and Materials
The diffusion tensor elements can be determined from at least six diffusion weighted images (Si) and one reference image(S0) without diffusion weighting. This examination is done by solving a set of linear equations: ln (Si / S0) = - SSbij DijDijrepresents the individual component of the symmetric 3x3 diffusion tensor. The b-matrix elements bij contain information about the specific combination of both the diffusion gradient and imaging gradient pulses. These elements are usually calculated by using a simplified equation (Eq. 1), which takes into account...
Results
The results of the first experiment are shown in Figure 1. The signal decay is plotted as a function of b. The solid line corresponds to the corrected signal decay from which the diffusion coefficient of D = 1.9 cm/s (water doped with 8.2 g CH3ZOONa and 9.3 g C3H5LiO3 on 1000 g H2O, T=20.5 C) was extracted. Deviations up to 10% were observed for several diffusion tensor elements after using the corrected b-values for extracting the diffusion coefficients. Figure 2. shows the correlation betweenthe...
Conclusion
The first experiment shows that the influences of inaccurately determined b-values are not negligible in diffusion weighted imaging. The contribution of imaging gradient pulses and corresponding cross-terms on the b-values is more prominent with weak diffusion gradients.However, determining the full diffusion tensor by taking into account all sequence gradient pulses is necessary in case of anisotropic media, such as the human brain.The resultsof thesecond part demonstrate that it is possible to determine the quality ofan application scheme by calculating the factor kappa. Applying the optimized...
References
M. Neeman et al.,"Effects of the imaging gradients on the determination of diffusion coefficients", J Magn Reson, 90, pp. 303, 1990J. Mattiello et al., "Analytical expression for the b matrix in MR diffusion imaging and spectroscopy", J Magn Reson, 108, pp. 131-141, 1994P.J. Basser, C. Pierpaoli, "A Simplified Method to Measure the Diffusion Tensor from Seven MR Images", MRM, 39, pp. 928-934, 1998N.G. Papadakis et al., "A Comparative Study of Acquisition Schemes for Diffusion Tensor Imaging Using MRI ", JMR, 137, pp. 67-82, 1999
Personal Information
D. Gllmar, J.R. ReichenbachInstitute of Diagnostic and Interventional Radiology - Friedrich-Schiller University - Jena/DEJ. HaueisenBiomagnetic Center/ Clinic of Neurology - Friedrich-Schiller University- Jena/DEThis study was supported by the Federal Ministry ofEducation and Research (BMBF) (Grant-No. 01ZZ0105)
